1. Field of the Invention
The present invention is generally related to a device for transferring power from a stationary device to a rotating device and, more particularly, to a power transferring arrangement that comprises primary and secondary coils of a transformer wherein one of the coils is rigidly attached to the stationary device and the other coil is rigidly attached to the rotating device and the coils are arranged in coaxial relation with each other.
2. Description of the Prior Art
Electrical power can be transferred from a stationary object to a moving object by using several known techniques. Carbon brushes are often used in various motor applications. In addition, the use of slip rings can provide electrical connection between stationary and moving objects. Rotating rectifiers, or brushless excitors, and rotating transformers can also be used to transfer electrical power between one object and another without requiring actual contact between stationary and moveable objects.
U.S. Pat. No. 5,227,942, which issued to Rourk on Jul. 13, 1993, discloses a structure for distributing failure induced transient currents in a multiphase electrical machine. It comprises an auxiliary stranded copper conductor that carries fault currents which are generated by a diode failure on the periphery of a brushless exciter diode wheel. The auxiliary conductor is constructed with a high frequency impedance that is lower than the adjacent diode wheel so that AC fault currents are diverted to the auxiliary conductor. The auxiliary conductor carries default currents to equalize both AC and DC flat currents among the fuse legs of the same phase. The auxiliary conductor can be circular and can be mounted between all of the diode fuse spaces at one end of the diode wheel and the diode wheel itself.
U.S. Pat. No. 5,180,923, which issued to Tyler on Jan. 19, 1993, describes a method and apparatus for downline load rejection sensing in a gas turbine control system. A speed signal representative of a turbine speed and a load signal representative of the turbine load are provided by the apparatus. The invention includes referencing devices for generating a delta speed reference signal and a delta load reference signal, derivative devices for determining the derivative of the speed signal and the load signal, comparators for comparing the speed derivative to the delta speed reference signal and for comparing the load derivative to the delta load reference signal and an indicator for indicating the occurrence of two events, namely, the first comparator determines that the speed derivative exceeds the delta speed reference signal and the second comparator determines that the load derivative exceeds the delta load reference signal. In one embodiment, a maximum turbine speed reference signal is provided and a third comparator compares a speed signal to the maximum turbine speed reference signal. An indicator provides a second indication on the occurrence of the first two events together with a third event, namely, a determination by the third comparator that the speed signal exceeds the maximum turbine speed signal.
U.S. Pat. No. 4,635,044, which issued to South on Jan. 6, 1987, discloses a failed fuse detector and detecting method for rotating electrical equipment. The apparatus is provided for remotely detecting the existence of a failed fuse of a brushless exciter rotor's rotating rectifier assembly. A conducting fuse produces a magnetic field which is sensed by elements of a stationary structure. A signal corresponding to the conducting status of each fuse is synchronized to the rotational speed of the brushless exciter rotor by means of a preselected oscillator frequency and the status of each individual fuse is retained and displayed until the next inspection of that fuse. Alarm circuitry enables automatic detection of a failed fuse and shut down in the event of multiple fuse failures. Since this method looks for the instance of current through each fuse, it operates in a fail-safe manner.
U.S. Pat. No. 4,336,486, which issued to Gorden et al on Jun. 22, 1982, describes a dynamoelectric machine with a brushless supplemental excitation system. Excitation power is supplied to a dynamoelectric machine by a main excitor having two field windings. A first field winding is driven by a pilot exciter which supplies base excitation for the main excitor. Forcing excitation is supplied by the second field winding which is driven by an external, supplemental power source. The main exciter can thus provide the appropriate excitation for both normal and transient operating conditions. In addition, by switching the controlled rectifier elements associated with the supplemental power source, the second field winding is also capable of providing fast de-excitation for the main exciter.
The four patents described above each relate to a brushless excitor, or rotating rectifier, that communicates electrical power between a stationary object and a rotating object. Each of the devices described in these patents depends upon, and makes extensive use of, the ferromagnetic structure which comprises iron that is associated with the winding of a coil structure. As will be described in greater detail below, the present invention does not use any ferromagnetic material in association with the winding for the purpose of providing a magnetic circuit between the primary and secondary windings.